Duke, who was chief operating officer at TowneBank in Portsmouth, Virginia, was confirmed by the Senate on June 27 to serve an unexpired term, ending Jan. 31, 2012, on the central bank's board.

Her swearing-in brings the normally seven-person board up to six and could give Fed Chairman Ben Bernanke a fresh ally for a steady policy course at a time a number of the regional Fed bank presidents are pushing for early rate hikes.

Bernanke has faced several dissents in recent months from other officials who have pushed for tighter policy.

While little is known on Duke's views on monetary policy, dissents by Fed board members are rare.

Fed board member Frederic Mishkin is due to step down to resume an academic career at the end of August.